Error: Can't use function return value in write context

[max-mathieu]

When configuration is missing the api key, PHP returns this weird PHP error "Can't use function return value in write context"

The issue seems to come from the use of empty in SparkPost.php: http://stackoverflow.com/a/2173318

[bazzmann]

We solved the fatal error removing the trim() function inside the empty one. (we are testing the library on a Drupal module).

Here is the code we used:

// Validate API key because its required
    if (!isset($settingsConfig['key']) || empty($settingsConfig['key'])){
    // Set as trimmed variable
    $APIKeyValidate = trim($settingsConfig['key']);
    if (!isset($APIKeyValidate) || empty($APIKeyValidate)){
      throw new \Exception('You must provide an API key');
    }

[lfbittencourt]

You can keep the one-line validation by using:

if (!isset($settingsConfig['key']) || !preg_match('/\S/', $settingsConfig['key'])){

The /\S/ regular expression have to match any non-space character to return true.